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    An analytical ultracentrifugation based study on the conformation of lambda carrageenan in aqueous solution
    (Elsevier Sci Ltd, 2013) Almutairi, Fahad M.; Adams, Gary G.; Kök, Mehmet Şamil; Lawson, Christopher J.; Gahler, Roland
    The conformation and heterogeneity of lambda-carrageenan, a sulphonated galactan from red seaweed, solubilised in aqueous solvent with the assistance of microwave irradiation, has been assessed by a combination of analytical ultracentrifugation, size-exclusion chromatography, light scattering and capillary viscometry. Preparations appeared generally unimodal on the basis of sedimentation coefficient distributions from sedimentation velocity although at the highest concentrations a shoulder appears with a sedimentation coefficient approximately 1.1 times greater than that of the main component. Even under conditions commensurate with charge suppression simple linear regression was insufficient to represent non-ideal concentration dependence and the extraction of the Gralen concentration dependence parameter k(s). A more general fitting algorithm was therefore employed. Mark-Houwink-Kuhn-Sakurada analysis of the change in intrinsic viscosity [eta] with molecular weight, together with the Wales-van Holde ratio (combination of k(s), with [eta]) point to an extended flexible conformation for lambda-carrageenan in the (weight average) molecular weight range M-w = 340,000-870,000 g/mol. The origin of the larger sedimentation coefficient component appearing at the higher concentrations is considered. (C) 2013 Elsevier Ltd. All rights reserved.
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    Application of recent advances in hydrodynamic methods for characterising mucins in solution
    (Springer, 2016) Almutairi, Fahad M.; Hernandez Cifre, Jose-Gines; Adams, Gary G.; Kök, Mehmet Şamil; Mackie, Alan R.
    Mucins are the primary macromolecular component of mucus-nature's natural lubricant-although they are poorly characterised heterogeneous substances. Recent advances in hydrodynamic methodology now offer the opportunity for gaining a better understanding of their solution properties. In this study a combination of such methods was used to provide increased understanding of a preparation of porcine intestinal mucin (PIM), MUC2 mucin, in terms of both heterogeneity and quantification of conformational flexibility. The new sedimentation equilibrium algorithm SEDFIT-MSTAR is applied to yield a weight average (over the whole distribution) molar mass of 7.1 x 10(6) g mol(-1), in complete agreement with size exclusion chromatography coupled with multi-angle light scattering (SEC-MALS), which yielded a value of 7.2 x 10(6) g mol(-1). Sedimentation velocity profiles show mucin to be very polydisperse, with a broad molar mass distribution obtained using the Extended Fujita algorithm, consistent with the elution profiles from SEC-MALS. On-line differential pressure viscometry coupled to the SEC-MALS was used to obtain the intrinsic viscosity [eta] as a function of molar mass. These data combined with sedimentation coefficient data into the global conformation algorithm HYDFIT show that PIM has a flexible linear structure, with persistence length L (p) similar to 10 nm and mass per unit length, M (L) similar to 2380 g mol(-1) nm(-1), consistent with a Wales-van Holde ratio of similar to 1.2 obtained from the concentration dependence of the sedimentation coefficient.
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    Hydrodynamic characterisation of chitosan and its interaction with two polyanions: DNA and xanthan
    (Elsevier Sci Ltd, 2015) Almutairi, Fahad M.; Erten, Tayyibe; Adams, Gary G.; Hayes, Maria; McLoughlin, Padraig; Kök, Mehmet Şamil
    Chitosan, a soluble polycationic derivative of insoluble chitin, has been widely considered for use in the food, cosmetic and pharmaceutical industries. Commercial ("C") and in-house laboratory ("L") prepared chitosan samples extracted from crustaceous shells with different molecular weight and degrees of acetylation (25% and 15%) were compared with regards to (i) weight-average molecular weight (M-w); (ii) sedimentation coefficient (s(20,w)(o)) distribution, and (iii) intrinsic viscosity ([eta]). These parameters were estimated using a combination of analytical ultracentrifugation (AUC), size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALS) and differential pressure viscometry. Polydisperse distributions were seen from sedimentation coefficient distributions and elution profiles from SEC-MALS. M-w values obtained for each sample by sedimentation equilibrium measurements were in excellent agreement with those obtained from SEC-MALS. Mark-Houwink-Kuhn-Sakurada (MHKS) and Wales van Holde analyses of the data all suggest a semi-flexible conformation. The principle of co-sedimentation was then used to monitor the interactions of the two different molecular weights of L chitosans with two polyanions, DNA and xanthan (another double helical high molecular weight molecule). Interactions were clearly observed and then quantified from the changes in the sedimentation coefficient distribution of the mixture compared to unmixed controls using sedimentation velocity. The interactions appeared to show a strong dependence on molecular weight. The relevance of this for DNA condensation applications is indicated. (C) 2014 Elsevier Ltd. All rights reserved.